In recent years, an energy storage apparatus provided with an energy storage device such as a battery (e.g., a lithium ion secondary battery or a nickel-metal hydride rechargeable battery) or a capacitor (e.g., an electric dual layer capacitor) has been used as a power source for a vehicle (e.g., an automobile or a motorcycle) or various kinds of equipment (e.g., a cellular phone or a notebook personal computer). The energy storage device for use in the energy storage apparatus of this type includes a case housing an electrode assembly therein and an external terminal disposed on an outer side of the case. The energy storage device is electrically connected to an adjacent energy storage device via a bus bar member to be welded to the external terminal. In this manner, the plurality of energy storage devices are electrically connected to each other, thereby constituting the energy storage apparatus. Moreover, the energy storage apparatus is connected to a motor or a control device, thereby constituting various kinds of equipment. The energy storage apparatus is exemplified by a lithium ion secondary battery module for use in an electric automobile or the like. This is an assembled battery constituted by connecting a plurality of lithium ion secondary batteries in series or parallel via bus bar members.
In an energy storage apparatus of this type, laser welding, for example, has been known as a method for welding an external terminal for an energy storage device to a bus bar member (e.g., JP-A-2013-33661). However, when an external terminal is welded to a bus bar member with a laser beam simply in the state in which the bus bar member is placed on an upper surface of the external terminal, the relative positional relationship between the external terminal and the bus bar member may be varied before or during the welding process. The phenomenon of the variation of the relative positional relationship between the external terminal and the bus bar member happens in various bonding methods such as resistant welding, ultrasonic welding, cold pressure welding, friction stir welding, and bonding with an adhesive agent, in addition to the laser welding